Silica, or basically silicon dioxide (SiO.sub.2), is an important article of commerce which is widely used in various industries, and which is available in a wide variety of forms for these uses. These various forms of silica include both hydrophilic and hydrophobic forms of silica. Hydrophilic silica, that is silica in the forms of silica gels (hydrogels), precipitated silica, fumed silica, diatomaceous earth and the like, has a wide variety of uses in industry. Silica gels, as well as these other forms of silica, are widely used as dehumidifying and dehydrating agents, in air conditioning, the drying of compressed air and other gases, as well as liquids, such as refrigerants, and oils containing water in suspension, for the recovery of natural gasoline from natural gas, for the bleaching of petroleum and natural oils, as catalysts and as catalyst carriers in chromatography and in other fields, as anti-caking agents in chemicals, cosmetics and pharmaceuticals, in waxes to prevent slipping, and in various dietary supplements.
These materials are generally produced from alkali silicate solutions, such as sodium silicate. These, in turn, are generally produced by reacting various alkali materials, such as sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, and others, with one of the various sources of silicon dioxide, such as natural quartz, diatomaceous earth, sand, flint and the like. This reaction is generally carried out in a high temperature furnace or in high temperature and high pressure reactors. Hydrogels are then generally produced by acidification with mineral acids and the like to precipitate the silica therefrom.
Hydrophobic silica in various forms has also become a staple article of commerce in a number of industries. Thus, hydrophobic silica materials, also known as organophilic silica materials, have become extremely useful as thickeners in organic substances such as resins, coatings, lacquers, paints and greases, and have been highly useful for dispersing materials on water surfaces or as defoaming agents, and anti-foaming agents. They are also formulated into various rubber compositions, used as an anti-caking material, and the like. In general, hydrophobic silicas are prepared from any of the well-known forms of hydrophilic silica, and generally by a process which affixes a hydrophobic material such as silicone or a polysiloxane oil or the like thereto. For example, U.S. Pat. Nos. 4,123,383 and 4,225,456 disclose the preparation of hydrophobic silicas by various methods including spraying silica particles with silicone oil and then heating at elevated temperatures of from about 250 to 350.degree. C. for one-half to about two hours. The silicone oils disclosed in these patents can be polysiloxane oils of various types, and the products are used in defoamer compositions in various aqueous systems. U.S. Pat. No. 4,443,357 discloses an improvement in these defoaming compositions which uses hydrophobic alcohols instead of organo-polysiloxanes to render the silica hydrophobic. Furthermore, U.S. Pat. No. 4,072,796 discloses the production of hydrophobic silica or silicates by a process which includes treatment with organo-halosilanes.
Miller et al, U.S. Pat. No. 3,714,068 discloses yet another hydrophobic silica composition for defoaming purposes, which in this case conditions the silica surface by controlling the proportion of hydrogen-bonded and physically absorbed water molecules on that surface, and in which hydrophobizing agents, such as silicone oils, silanes, and alcohol esters are employed to replace the water molecules.
The assignee of the present application, the silica products group of MMII Incorporated, sells a commercial product designated "Grade 60Zr Sodium Zirconia Silica," which is a blend of amorphous silica, zirconium silica hydrogel, and other zirconium species, such as zircon, and which is used for anti-caking, flow conditioning, as a liquid carrier, and as a functional filler material. This hydrophilic material is prepared from the byproduct of a commercial zirconium recovery process of Magnesium Elektron Inc. of Flemington, N.J. In that process a zircon sand containing about 66 wt. % zirconium is reacted with soda ash, or sodium carbonate, at elevated temperatures of about 1,000.degree. C. so as to create a soluble form of the zirconium. This fused form of sodium zirconyl silicate is then treated with concentrated hydrochloric or sulfuric acid in a leaching step intended to extract as much of the zirconium from this material as is possible. Thus, about 60% to 95% of the zirconium is solubilized and removed, with the remainder left in the form of a blend of silica gel, and a portion of a co-precipitated silica-zirconium gel, as well as some unreacted zircon. It is this material which has previously been discarded, but which the assignee of the present application has employed as a source of the blend constituting the commercial product identified above.
It is also well known that zirconium in various forms has utility for a number of compositions, many of which are ceramic and glass compositions. Reference is made in this regard to Guglielmi et al, "Deposition of silica-zirconium coatings on glass fibers by the sol-gel method,"Ist. Chim. Ind., Univ. Padova, Padua, Italy, Riv. Stn. Sper. Vetro (Murano, Italy) 1984, 14(6), 241-3. Also, dentifrices containing synthetic amorphous zirconium-bound silicates as abrasives which are stable during storage are disclosed in "Dentifrices containing zirconium-bound silicic acid salts," as disclosed in Japanese Patent Publication No. 60 48,017 (see Chemical Abstracts, 103:76093y, vol. 103, 1985, p. 314). Furthermore, in Glenz, "Investigation of the mechanism of rendering textiles hydrophobic with silicones," Melliand Textilber, 41, 1125-9(1960), it is disclosed that cotton fibers were impregnated with a mixture of dimethyl polysiloxane derived silicones and aged methyl polysiloxane derived silicones containing zirconium compounds, which caused complete glassification of the fiber surfaces and good water repellency. However, this author specifically states that in this environment attempts to form the film in the absence of the fibers resulted in failures, and that silicone emulsions showed no substantivity toward cotton. This author thus certainly did not produce or even suggest the production of a zirconium silica hydrogel in this article.
Stabilized, porous silica bodies are disclosed in U.S. Pat. No. 4,600,646. In this patent chromatographic packings are disclosed which include specified porous silica bodies, or silica micropheres, which are contacted with various metal compounds so as to cover these spheres with a partial surface covering of metal oxide, including zirconium oxide, which are thereby hydrolytically stabilized for later chromatographic use The particular silica microspheres to which this patent are directed are known a ZORBAX packings (registered trademark of E. I. duPont de Nemours Co., Inc.) which are produced by a specific process as set forth at column 2, lines 46-64 of the '646 patent. This patent also then discloses the use of organosilane coatings to provide the desired chromatographic packing material. It can therefore be seen that there has been some utilization of zirconium compounds in various fields, and particularly those which also employ silicon chemistry for a number of purposes, but none of these developments have been based upon any general recognition of the possibility of utilizing zirconium to produce silica hydrogels having improved stability, and certainly not the myriad of potential commercially significant uses of such materials as a substitute for the silica products currently constituting almost the entire market for these compounds.